The Massachusetts Invasive Species War is Justified

Water Chestnuts in the Sudbury River, photograph by Ann Ringwood for Wicked Local 

There’s some curious reasoning in “The invasive species war,” an “Ideas” piece on plants and attitudes that ran in last Sunday’s Boston Globe. After spending two paragraphs detailing the valiant efforts Charles River Watershed Association volunteers make to remove water chestnuts from the Charles river, writer Leon Neyfakh states:

“The reasons to fight invasive species may be economic, or conservationist, or just practical, but underneath all these efforts is a potent and galvanizing idea: that if we work hard enough to keep foreign species from infiltrating habitats where they might do harm, we can help nature heal from the damage we humans have done to it as a civilization… If we’re going to help restore a more natural environment, how do we decide what in the world is ‘natural’ and what is the result of artificial forces? ”

Those are rather odd statements to make in the context of water chestnuts. The Charles River Watershed Association doesn’t use the word “foreign” in its page on water chestnuts. They use the word “invasive,” which is description of the plants’ behavior; water chestnuts invade new areas, grow more quickly than other aquatic plants, and eliminate their competitors by shading or strangling them out. Is there another polite word for what these plants do? “Total war” seems a bit extreme.

Water Chestnut “Mats”, photograph by Karen Knee of Philly.com

As for “artificial forces”—I’d say that water chestnuts  produce damage done by nature to nature. In case you’ve never seen water chestnuts in (very slow) action, here’s a brief description of their charming growth habits from the National Park Service.

“Water chestnut can form dense floating mats, severely limiting light – a critical element of aquatic ecosystems. Once established, it can reduce oxygen levels, increasing the potential for fish kills. It competes with native vegetation and is of little value to waterfowl. Water chestnut infestations limit boating, fishing, swimming and other recreational activities. Further, its sharp fruits, if stepped on, can cause painful wounds.”

In short, left to themselves, water chestnuts can transform the Charles River, the Arlington Reservoir, the Sudbury River, and pretty much any other fresh-water body in Massachusetts into water-chestnut farms. They’ll make is so you can’t boat or swim, fish die off from lack of oxygen, and ducks have nothing to eat–with no help from humans at all. Granted, humans brought them to the U.S. in the first place; these natives of Asia and Europe were first observed near Concord, MA in 1859.

Invasive Water Chestnuts, photographs by Leslie Mehrhoff

Once he’s done with the water chestnuts (if only the Charles River Watershed Association could be done with water chestnuts!), Neyfakh goes on to describe claims that the division of plants into “native” and “non-native” is roughly the product of anti-immigrant bias. He quotes Hugh Raffles, an anthropologist at the New School, saying,  “We choose to designate some plants and animals as native because they fit with the way that we want the landscape to look.”

That’s a fine explanation—if all you do is look at the landscape. If you examine the ecology, though, you’ll find that there are real, important, and measurable ways that non-native plants affect life around them.

According to Douglas Tallamy, chair of the Entomology and Wildlife Ecology department at the University of Delaware, when you replace native plants with non-native plants, you destroy the food chain. Here’s how it works, from Tallamy’s Bringing Nature Home web site.

“With few exceptions, only insect species that have shared a long evolutionary history with a particular plant lineage have developed the physiological adaptations required to digest the chemicals in their host’s leaves. They have specialized over time to eat only the plants sharing those particular chemicals. When we present insects from Pennsylvania with plants that evolved on another continent, chances are those insects will be unable to eat them. We used to think this was good. Kill all insects before they eat our plants! But an insect that cannot eat part of a leaf cannot fulfill its role in the food web. We have planted Kousa dogwood, a species from China that supports no insect herbivores, instead of our native flowering dogwood (Cornus florida) that supports 117 species of moths and butterflies alone.”

New England Aster, Photograph by Frank Mayfield

Solidago Goldenrod, photograph by Sue Sweeney

Tallamy provides lists of the species that support the most insects. Oaks, black cherries, goldenrods and asters top the list. But when was the last time you saw goldenrod for sale at Home Depot?

Given that 95% of the land in the United States is now used for cities, suburbs, agriculture, or harvested for timber, those insects aren’t getting a lot of food. Every acre of lawn—and there are more than 40 million acres of lawn in the U.S., according to Tallamy—means that there are fewer leaves that caterpillars can eat. Birds rely on a good supply of caterpillars to feed their chicks; fewer caterpillars means fewer chicks survive. If the bird population is already low to begin with, that could mean extinction.

Caterplllar, photograph from the Tyler Arboretum

And frankly, Massachusetts birds need help. According to the North American Breeding Bird Survey, more than one-third of the inland birds surveyed in Massachusetts showed “significant negative trend” between 1966-2009. The population of bobwhites went down by more than ten percent a year. Massachusetts Audubon refers to bobwhites’ “virtual disappearance.”

What’s more, non-native species are getting more and more land every day. According to Massachusetts Audubon’s report Losing Ground, between 1999-2005, 40,000 acres of land in the state were developed; 30,000 acres from former forest, 10,000 acres from farms. Those home and business owners probably aren’t planting choke cherries and swamp white oak to feed the butterflies. They’ll put in lawns with non-native grasses, New Guinea impatiens, hostas, an Asian rhododendron or two and forsythia. None of these plants are native, and none of them will support the local web of life. As far as butterflies and birds are concerned, they’re green plastic.

Studies on “species richness,” or how many different species live in an area, bear Tallamy’s theories out. For example, Michael McKinney’s analysis of studies of urban and suburban areas showed, unsurprisingly, that center cities reduce species richness. Creating suburbs, though, increases the number of types of plants (since you’re adding marigolds to the milkweed), but reduces the number of types of insects and other animals. Presumably, they’re starving.

In short, you can make all the declarations you like about how words like “invasive” and “non-native” express human values, but it won’t make a spicebush swallowtail butterfly eat your petunias. That’s the difference between non-native and native plants. Humans value the imports; everything else prefers their plants home-grown. (Doug Tallamy just shows what’s on the menu.)

Female Spicebush Swallowtail, photograph by Megan McCarty

And yes, it is a human value to decide that it’s better to have more different species around rather than fewer.  What can I say? I’m not a botanical moral relativist. I want enough edible plants around for the swallowtails, and fritillaries, and hairstreaks, and checkerspots, and mourning cloaks, and painted ladies. I’m willing to go to war with Massachusetts’ invasive non-native plants to make sure they do not starve. I think in this case, war is justified. I suspect our local skippers, and admirals would agree.

  7 Replies to “The Massachusetts Invasive Species War is Justified”

  1. Leslie Turek
    August 1, 2011 at 7:32 pm

    Meg, I’m so glad you wrote this. I saw that article and I thought it was very superficial. You have clearly presented some of the issues on the other side. I wonder if you might have the time to write a short letter to the editor making some of these points? It really would be good to have the other side presented in the same forum.

  2. Meg
    August 2, 2011 at 10:08 am

    Leslie – Thank you. I sent a letter to the Globe too.
    There’s a good video of water chestnuts on the Nashua river here:
    http://www.nashuatelegraph.com/news/927836-196/could-the-nashua-river-turn-into-water.html

  3. Kathy Hoben
    August 5, 2011 at 10:19 am

    Meg,
    Thank you for writing that piece. I had only thought about invasive species impact on other plants. But, of course, it impacts wildlife and the food chain. Very well written and researched.

  4. August 7, 2011 at 11:36 pm

    Just as the strongest argument against nativism isn’t that it is rooted in anti-immigration sentiment, the strongest argument in support of it isn’t “co-evolution.” There are few mutually exclusive relationships between plants and animals in nature that result from “co-evolution” because it is a risky survival strategy in a world that is constantly changing. If, for example, the specific plant upon which a specific animal depends doesn’t bloom or doesn’t return from its dormant phase because of a sudden, even temporary, change in the climate, the animal that is dependent upon that plant is out of luck. Such relationships therefore do not persist in nature. Species that survive have “back-ups” such as many different pollinators for a particular plant. And adaptation and evolution enable both plants and animals to change (over generations) in response to changes in the environment. Nature is resilient and opportunistic.

    Here on the West Coast, Professor Art Shapiro (UC Davis) has found exactly the opposite of Doug Tallamy. That is, he has found that where non-native plants dominate on the coast the butterflies have adapted to them and in some cases they are now multivoltine because the non-natives are available most of the year unlike the natives that were dormant during the dry season.

    The strongest argument against nativism is that it is doing more harm than good. Nativism is destroying millions of trees just because they aren’t native even though they are doing no harm to plants or animals. It is using herbicides in public parks for the sole purpose of eradicating non-native plants and prescribed burns that pollute our air and endanger our homes. Unless nativism can make the necessary distinction between non-native species that are actually doing any harm and those that are not, it is damaging our environment needlessly. In the San Francisco Bay Area, there is no doubt that the native plant movement is doing a great deal of unnecessary harm. Read about these destructive projects: http://milliontrees.wordpress.com.

  5. Meg
    August 8, 2011 at 3:54 pm

    Million Trees– First of all, that’s obviously not your name, and there’s no indication of who’s writing your blog on your web site, or how to contact you apart from leaving a message at your site. Consider correcting that. I have more confidence in political information when I know who’s paying for it.

    As to your comment here: nature is resilient and opportunistic over the long term. Here on the East Coast, though, we are seeing massive turnovers in species dominance in vast areas over the course of a decade, sometimes only a few years, largely caused by human intervention. Water chestnuts didn’t just up and walk across the Atlantic; we brought them here.

    You say that “Species that survive have “back-ups” such as many different pollinators for a particular plant.”– but those “back-ups” are often *also* native plants, which are being replaced with petunias and soybeans. That isn’t even taking account of the species that have already disappeared from eastern ecosystems like the chestnut trees that used to make up a quarter of our forests.

    I can’t speak to projects taking place on the West Coast; you’re in a completely different ecosystem with very different imperatives. We don’t have dry-season wildfires in Massachusetts, because there *is* no dry season, and I suspect that east-coast insects are far less opportunistic feeders than west coast specimens because of that very fact.

    As for baseless nativism–around Boston, non-native species like water chestnut and Asiatic bittersweet are clearly doing considerable harm to plants and animals. They’re also blocking boat traffic on waterways and taking down electrical lines when vine-weighted trees finally collapse. It’s hard for me to have sympathy for that kind of destruction.

  6. November 14, 2011 at 4:27 pm

    Bravo! Thanks for laying out very clearly the basis and evidence in support of the hard work ahead for generations, if this and other invasives are to be managed (they will never be eradicated, of course)
    The ignorance of “relativism” in this (and many other) domains allows further loss of our native bio-diversity in the name of ‘live and let live’ or, ‘who are we to decide’.
    It is an example of unfortunate culture-guilt that some of (us of) European or further eastern descent may be offended by yet another example of ‘our’ decidedly less than constructive contributions to the hemisphere which we now inhabit.

    I’ve often thought about how apt a symbol of manifest destiny is the lovely dandelion. Itself a prized pot-and-salad herb in Europe and a hardy medicinal, yet spread without regard across the new world by the billions of floating seeds to the detriment of the natives which it displaced. (Of course, with potent poetic justice, it also upends the Eurocentered dream of perfect green lawns!)

  7. Meg Muckenhoupt
    November 14, 2011 at 5:56 pm

    Thank you!

    Ah, but dandelions co-exist with all manner of other plants; you never see a field that consists entirely of dandelions the way you see monocultures of purple loosestrife, garlic mustard, buckthorn, even Norway Maples (I saw one on Peddocks Island a few years go–near what was the northernmost infestation of kudzu at the time!). A monoculture field of dandelions would be a pretty astonishing sight.

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